STRUCTURE AND METAMORPHISM OF THE CALLIOPE VOLCANIC ASSEMBLAGE - IMPLICATIONS FOR MIDDLE TO LATE DEVONIAN OROGENY IN THE NORTHERN NEW-ENGLAND FOLD BELT

The Late Silurian to Middle Devonian Calliope Volcanic Assemblage in t he Rockhampton region is deformed into a set of northwest-trending gen tly plunging folds with steep axial plane cleavage, Folds become tight er and cleavage intensifies towards the bounding Yarrol Fault to the e ast. These folds and associated cleavage also deformed Carboniferous a nd Permian rocks, and the age of this deformation is Middle to Late Pe rmian (Hunter Bowen Orogeny). In the Stanage Bay area, both the Callio pe Volcanic Assemblage and younger strata generally have one cleavage, although here it strikes north to northeast. This cleavage is also co nsidered to be of Hunter Bowen age. Metamorphic grade in the Calliope Volcanic Assemblage ranges from prehnite-pumpellyite to greenschist fa cies, with higher grades in the more strongly cleaved rocks. In the Ro ckhampton region the Calliope Volcanic Assemblage is part of a west-ve rgent fold and thrust belt, the Yarrol Fault representing a major thru st within this system. A Late Devonian unconformity followed minor fol ding of the Calliope Volcanic Assemblage, but no cleavage was formed. The unconformity does not represent a collision between an exotic isla nd arc and continental Australia as previously suggested.